Administration of intravenous fluids to a patient is well known in the art. Typically, a solution such as saline, glucose or electrolyte in a glass or flexible container is fed to a patient's venous access site via a length of flexible plastic tubing such as polyvinyl chloride (PVC) tubing. The rate of flow of the fluid is controlled by a roller clamp which is adjusted to restrict the flow lumen of the tubing until the desired flow rate is obtained.
Flow from the container to the patient may also be regulated by means other than a roller clamp. It is becoming more and more common to use an electronically controlled pump. One type of pump that is used for intravenous fluid administration is a peristaltic-type pump.
Use of peristaltic pumping action is particularly well suited for the medical field. This is because peristaltic pumping action can be applied externally of the tubing carrying the intravenous fluid. This maintains the sterile condition of the intravenous fluid within the tubing while imparting fluid propulsion on the fluid. The peristaltic pumping action can also be applied at any point on the tubing.
In a common type of peristaltic pump used in the medical field, a driving motor is connected to an array of cams angularly spaced from each other. The cams in turn drive cam followers which are connected to corresponding pressure fingers. These elements cooperate to impart a linear wave motion on the pressure fingers. A pressure plate is secured juxtaposed to and spaced from the pressure fingers. The pressure plate holds the tubing against the reciprocating pressure fingers to impart the wave motion on the tubing to propel the fluid. Alternatively, the driving motor drives a rotary-type peristaltic pump in which a plurality of rollers contact the tubing to impart fluid propulsion. A pressure plate holds the tubing adjacent to the rollers.
In a preferred embodiment of peristaltic pumps, the driving motor is a stepping motor which rotates in small increments or steps. While a stepping motor rotating at a high rate of speed gives a visual impression that the rotation is constant, the stepping motor in fact turns through a series of small angular increments or steps which are followed by a brief period of rest. In stepping motors utilized in peristaltic pumps in the medical field, these small angular steps can range from about 0.36.degree. to 7.2.degree. and in a preferred embodiment are about 1.8.degree.. This results in a series of steps of the shaft between 1000 and 50 per revolution or, in the preferred embodiment, about 200 steps per revolution.
In these prior art devices, the stepper motor was driven conventionally to impart the fluid propulsion on the pressure fingers or rollers. A drawback in such devices is the use of a large amount of power which resulted in use of large power sources such as batteries and a limited infusion time.
Additionally, different drive methods are also preferably utilized which are commonly referred to as wave drive, half step drive, and full step drive. In this prior art, these different step driving signals were the only possible driving methods available to effectuate a coordination of power control to provide measuring motor torque.
Further, in pumps of the prior art, the power feeding the driving motor needed to be reduced by absorptive lumped or active elements or was reduced by adjusting the voltage to the motor using a feedback microprocessing means.
What would thus be desirable is a peristaltic pumping apparatus in which a wide variety of stepping frequencies and a new inventive modulation means be provided in an efficient manner to provide a very wide range of infusion rates, including microinfusion. It would further be desirable for the peristaltic pumping apparatus to reduce the amount of power needed to drive the stepping motor without using absorptive or lumped elements. It would be still further desirable for the peristaltic pumping apparatus to automatically provide instantly and safely the required power compensation to the stepping motor. The present invention provides such a device.